A micro hardness test or a super-micro hardness test, which can examine a mechanical property of a microstructure of a material, are expansively used as a measurement method of a material in wide fields such as semiconductor and micro machining in recent years.
In the micro hardness test or the super-micro hardness test (hereinafter, simply called micro hardness test and the like), a method is widely used, in which a relationship between indentation force (F) and indentation depth (h) in an indentation process of indenting an indenter into a surface of a sample, so-called an indentation curve is obtained to measure a property of a material such as hardness. This is because since size of impression produced in a surface of the sample is extremely small in the micro hardness test and the like, 1 μm or less, compared with a macro hardness test such as the Vickers hardness test, size of impression is hardly measured by a light microscope.
Moreover, in the micro hardness test and the like, it is not sufficient only to obtain indentation depth at the maximum load when the indenter is indented into the sample, and it is required to obtain a relationship between continuous indentation force from load to unload and indentation depth, that is, an indentation curve, as schematically shown in FIG. 1.
Furthermore, to evaluate a property of a material from the indentation curve obtained in this way, in some cases, it is enough to simply compare the magnitude of the indentation depth at the maximum indentation force and the like, however, in other some cases, the indentation curve is used for fitting to a particular function form in order to calculate shape compensation of the indenter or a parameter such as hardness (for example, see patent literatures 1 and 2), or used for determining a position of a characteristic point as schematically shown in FIG. 2 (for example, see patent literature 3). In this case, a more accurate indentation curve having no blank and high data point density is required.
As a method of obtaining such an indentation curve, a load test by one of (A) load (indentation force) control method, or (B) displacement (indentation depth) control method is generally performed. The (A) load control method or the (B) displacement control method is for discretely obtaining a relationship between load and displacement by measuring displacement or load while controlling a tester such that a load range (df) applied to a sample or a displacement range (dh) is to be a certain setting value, respectively. FIGS. 3 and 4 schematically show indentation curves obtained by the (A) load control method and the (B) displacement control method respectively, and show actually measured points (data points) by black circles. As known from FIGS. 3 and 4, the (A) load control method has a feature that the data point density is typically high compared with the displacement control method in a large gradient region of the indentation curve, for example, at a high load side and in an unloading process, or in a case of a hard sample, and stable control can be performed compared with the displacement control method. In a typical hardness test, results at the same load are traditionally compared in many cases, and results at various levels of load below specified load can be obtained by the method. The other (B) displacement control method has a feature that the data point density is typically high compared with the load control method in a small gradient region of the indentation curve, for example, at a low load side or in a case of a soft sample.
(For example, refer to patent literature 3, non-patent literature 2, and non-patent literature 3.)
[Patent literature 1] JP-A-11-271202.
[Patent literature 2] JP-A-9-318516.
[Patent literature 3] JP-A-2004-81546.
However, in an actual micro hardness test and the like, since the gradient of the indentation curve is different between hard and soft portions of a sample, an optimum load range (df) or displacement range (dh) is different depending on a measurement place. Specifically, in the case of the load control method, since the gradient of the indentation curve is large in a test at a hard portion, the load range (df) can be set relatively large, however, the load range (df) needs to be conversely decreased in a test at a soft portion. Here, when the sample is uniform, the optimum load range (df) can be determined by performing tests several times. However, when the sample is not uniform, for example, when hardness has distribution, there have been problems that since results are essentially different depending on places, the test must be performed at an unnecessary small load range (df) on the assumption that the softest portion may be tested to secure a certain data point density, consequently much time is required for measurement, and the test is easily influenced by temperature drift. Such problems are the same in the displacement control method in which sufficient data point density is not obtained for various indentation curves having different gradients, or an experiment at an unnecessarily small displacement range (dh) is forced to be conducted.
Moreover, in the case of the indentation curve having the characteristic point as shown in FIG. 2, there has been a problem that the optimum load range (df) or displacement range (dh) is hard to be set in the case that a position of the characteristic point can not be expected.
Thus, the invention of the application was made in the light of the circumstances as above, and has an issue of providing a new production method of the indentation curve, which solves the problems in the related art, and enables securing sufficient data point density in various indentation curves having different gradients without changing setting by an observer, and a new micro hardness test method.